Common Medicare billing denials

A Medicare denial is distinct from a claim rejection. A rejection means the claim did not pass front-end edits and was never accepted into the processing system, while a denial means the claim was accepted, adjudicated, and then declined for payment. The categories that recur most often in Medicare fee-for-service are structural: they reflect the program's rules on who is eligible, what is covered, who may bill, and how Medicare coordinates with other payers. Medicare Advantage (Part C) plans apply their own claim-processing rules on top of Medicare's framework, so denial patterns there can differ; that distinction is covered in Medicare Advantage (Part C) billing.

Every denial is expressed through standardized code sets — claim adjustment reason codes (CARCs) and remittance advice remark codes (RARCs), maintained under X12 governance — that appear on the remittance advice (ERA). These codes name the reason and frequently point toward the fix. Interpreting them is the subject of Reading the Medicare remittance and MSN.

One of the most common categories involves the beneficiary's identity and coverage status. If the Medicare Beneficiary Identifier (MBI) is missing, mistyped, or no longer valid, or if the beneficiary was not entitled to the billed benefit on the date of service, the claim is denied. These denials are largely preventable through eligibility verification before the visit, which confirms active entitlement and the correct identifier. General workflow guidance lives in the eligibility verification cluster, and Medicare-specific steps in verifying Medicare eligibility.

• Invalid or outdated MBI, including format errors or an identifier reissued after the date of service
• Beneficiary not entitled to the specific Part A or Part B benefit on the date of service
• Name or date-of-birth mismatch against Medicare's records
• Service billed to the wrong Medicare entity when another payer was primary

Identifier and eligibility denials are usually administrative: once the correct information is confirmed, the claim can typically be corrected and resubmitted, subject to the applicable filing deadline discussed below.

A large share of Medicare denials concern whether a service is covered and supported as reasonable and necessary. Medicare coverage is defined through national coverage determinations and, within each contractor's jurisdiction, through a local coverage determination (LCD). When a service falls outside those criteria — or when the documentation does not establish medical necessity — the claim is denied. The framework of these determinations is explained in National and local coverage determinations.

Medical-necessity denials often turn on the linkage between the service billed and the diagnosis reported, on frequency limits, or on documentation that does not reflect the coverage criteria. The corrective path depends on the underlying cause: a documentation gap may be addressed on appeal with supporting records, a coding-linkage issue may be corrected, and a genuinely non-covered service may not be payable by Medicare at all. When a provider expects a service may be denied as not reasonable and necessary, an Advance Beneficiary Notice (ABN) may shift financial responsibility to the beneficiary; its rules are detailed in The Advance Beneficiary Notice (ABN).

Denials in this category stem from who is billing and how Medicare relates to other coverage. If a provider lacks active Medicare billing privileges, or if the enrollment record in PECOS does not support the billed service or reassignment, claims are denied. The connection between provider enrollment and payment is covered in Medicare enrollment and billing privileges, and the role of assignment in Assignment and participation.

A separate and frequent source of denials is coordination of benefits. Under Medicare Secondary Payer (MSP) rules, Medicare is not always the primary payer; when another payer is primary and the claim is submitted to Medicare first, or without the primary payer's adjudication, Medicare denies it. MSP situations and the questionnaire process are covered in Medicare Secondary Payer (MSP) billing. Some denials also flag a missing or incorrect prior authorization, which applies to specific services and settings rather than universally.

Enrollment denial

The billing or rendering provider does not have active, appropriate Medicare billing privileges for the service or the reassignment on record in PECOS.

Assignment-related denial

Payment or claim handling does not match the provider's participation and assignment status for the service.

MSP denial

Another payer is primary under coordination-of-benefits rules, so Medicare declines to pay as primary until the primary payer has adjudicated.

Medicare will deny a claim submitted after its filing deadline regardless of the claim's clinical merit. The standard filing period and the limited exceptions are set by CMS and explained in Medicare timely filing; because the period is measured from the date of service and has narrow exceptions, the current CMS rule is the authority rather than any assumed number of days. Other administrative denials involve duplicate submissions, incomplete claim fields, or the wrong claim form for the setting — the professional CMS-1500 versus the institutional UB-04.

Distinguishing a correctable administrative denial from one that requires the formal appeals process is the core denial-management decision. The reason and remark codes on the remittance advice generally indicate which path applies, and the broader mechanics of both are covered in the denials and appeals cluster.